So long as it is in /etc/tmp*.d/<whatver> or the /usr/lib equivalent it will
be recreated by systemd-tmpfiles on every boot. As the man page says, you've
read that, I presume, if you don't want that action you symlink the relevant
filename to /dev/null.

I don't understand this. Symlink /media to dev/null?

Carlos, the only way you will stop that is to remove the relevant file or
symlinking it.

So why isn't/usr/lib/systemd/system/tmp.mount being used?
Cristian has pointed out previously in this list that openSuse has been
modified so that it isn't. HOW? you ask? That is what Andrey has been
telling you!

Because /usr/lib/tmpfiles.d/tmp.conf is creating them first.

Ok, so if I want /media to be a tmpfs, either I bind-mount it to
somewhere, or create it with a service like
"/etc/systemd/system/media.mount similar to
"/usr/lib/systemd/system/var-run.mount".

Right?

Hmm, no, "/usr/lib/systemd/system/var-run.mount" creates a bind from
"/run" to /var/run". Then where is "/run" created?

I could, then, create a directory under "/run", and mount-bind "/media" to
it. Or create an entire new tmpfs.